For some time now there has been a need for a better method to reduce the cost for making longitudinal welds on beams and columns and for making circumferential and longitudinal welds on heavy wall vessels. A faster method could improve the economics for making long welds on heavy plate. These longitudinal and circumferential welds are generally one of four types: (1) horizontal fillet weld, (2) fully positioned fillet welds, (3) full penetration groove welds, or (4) partial penetration groove welds. These welds have traditionally been produced with either multi-pass submerged arc, or multi-pass flux-cored wire, on plate thicknesses ranging from ⅜″ thick to 4.00″ thick and up.
The drawbacks to the conventional multi-pass submerged welding is the: (1) Increased number of passes required to fill up the weld: (2) Increased consumption of welding flux to complete the weld, (3) Increased time required to remove the flux slag after each pass and, (4) Increased time it takes to complete the weld to maintain weld soundness and mechanical properties commensurate with the properties required by the AWS D1.1 Structural Code, and the AWS D1.8 Seismic Code, or the AWS D1.5 Bridge welding codes.
In the conventional submerged arc welding (SAW) process, less than 20% of the arc energy is utilized in melting the electrode wire. The remainder is: (1) dissipated in melting the base plate and welding flux, (2) used in superheating the weld pool, (3) lost in overheating the plate, and (4) lost in the atmosphere. During the melting of welding flux and base plate, the arc energy expended in superheating the weld pool and creating excessive fusion in the base plate is harmful and undesirable. The excessive melting of the base plate results in deeper penetration, larger heat affected zone (undesirable), and higher dilution; therefore, a system and method for better utilization of the arc energy is needed.
When welding with higher amperages, to increase the rate of deposition, higher heat input on groove welds and fillet welds are required, using the single wire, dual-wire (two wires in one single torch), or tandem wire DC/AC (two torches in tandem). Increased heat input causes the welding flux to lock into the wet lines (where the weld metal meets the parent material) using the multi-pass welding technique. Removing the welding flux from each weld pass requires careful and time consuming slag removal and clean up after each pass. If the residual flux is not completely removed from each pass, the flux can be included into the resultant weld, causing a defects that may be extremely expensive to repair, To solve the problem created by high heat input welds, locking flux into the wet lines, the operator generally uses smaller multi-pass welds to eliminate the problem. This solution results in lower amperages, lower deposition rates, and thus more expensive welds.
In an effort to improve the welding economics for longitudinal heavy plate welds, while still maintaining quality, Arcmatic™ has developed a high amperage, high deposition, single or multi-pass variation of submerged arc welding called “High Deposition Submerged Arc plus Metal Powder” (HD-SubArc+MP™). This Arcmatic™ process uses 1/16-inch, 5/64-inch, 3/32-inch, ⅛-inch, or 5/32-inch (or the metric equivalent) diameter welding wires, in a single torch (dual-wire), or two dual-wire torches in tandem (one torch behind the other). The process uses very high current density, in conjunction with a metal powder additive in the weld joint.
The very high current is provided with two constant voltage DC welding power supplies connected in parallel, or two square wave AC power supplies connected in parallel.
This welding system and method is capable of producing a full penetration groove weld, or a single pass fillet welds on plate thickness (up to 1.50 inch thick) in one single pass, from one side. Based on production experience, the HD-SubArc+MP™ welding system and welding method offers tremendous advantages over a traditional single-wire, dual-wire or tandem-wire submerged arc weld.
The HD-SubArc+MP™ welding system is not a pre-approved process and must be accompanied by developing a Welding Procedure Specification (WPS) and a Procedure Qualification Record (PQR,) as outlined in the AWS D1.1 Structural Steel Welding Code, the AWS D1.8 Seismic Welding Code, and/or the AWS D1.5 Bridge Welding Code—whichever applies.
An object of the HD-SubArc+MP™ welding system and method is to increase the depth of each weld pass when making a Multipass weld, or increasing the thickness of plate that can be welded in a single pass; thus increasing the deposition rate, minimizing the clean-up after each pass, reducing the consumption of flux, with the goal in mind of making a more economical weld.
These properties will, in many cases, allow one-sided submerged arc welding of thick steel plates by using a specially formulated welding flux that will meets all the conditions listed above.
Another advantage of the HD-SubArc+MP™ welding system and method is that it is able to overcome the problems associated with other high amperage submerged arc welding process, such as: (1) inability to remove the flux from the wet lines, (2) creating rejects as a result of flux inclusions in the resultant weld bead, or (3) generating cracks in the weld created by the high heat inputs.
A further objective of the Arcmatic HD-SubArc+MP™ welding system is to provide a system and method that creates better control of the weld bead shape, minimize base metal dilution, reduce the total heat input into the parent material, and the reduce or eliminate any magnetic field that can deflect the welding arc, resulting in a weld defect.
Additional objectives of the HD-SubArc+MP™ welding system and method is to provide a method that is capable of efficiently making a single-pass weld, or a multi-pass weld for both longitudinal and circumferential welds on thick, heavy plate steel on beams, columns, vessels, and like structures.
The HD-SubArc+MP™ welding process incorporated Narrow Gap and/or Narrow Groove welding. Narrow Gap welding process incorporates two plates welded together. The two plates are welded using two square cut plates, spaced between ⅜-inch to 518-inch apart and the gap between the two square cut plates is filled with metal powder prior to using the HD-SubArc+MP™ welding process. The Narrow Groove welding process involves beveling each of the two plates with a smaller bevel than is generally used in a multi-pass welding process. Standard weld joints generally use between 30-to-45-degree included angle with a ¼-to-⅜-inch root opening. The Narrow Groove welding process used with HD-SubArc+MP™ generally incorporates a ⅜-inch root opening with a 15-degree included angle or less. This allows the two plates to be joined together using much less filler metal lower heat inputs, and uses much less time to make the weld.
Using the Arcmatic™ HD-SubArc metal powder welding systems, a variety of welding joints can be welded, including horizontal fillet welds, fully positioned fillet welds, multipass groove welds, single pass groove welds, double bevel groove welds, single bevel groove welds, full penetration groove welds, and full penetration groove welds. This large variety of welding grooves may be necessary in the fabrication of structural steel box columns, bridge girders, buildup columns, heavy-wall pressure vessels, wind towers and like structures, offshore platforms, shipbuilding panel line fabrication, etc. These structures are readily fabricated using the HD-SubArc+MP™ process.